A liquid crystal projector includes: a plurality of dichroic mirrors for separating the light of luminous flux from a light source into the luminous flux of each of the colors red (R), green (G), and blue (B); three liquid crystal panels upon which is irradiated the luminous flux of each color that was color-separated; a color-synthesizing prism for color synthesis of image light of each color that is modulated by spatial arrangement in each liquid crystal panel; and projection optics for projecting the image light that has been color-synthesized onto a screen.
A liquid crystal panel is provided with a plurality of liquid crystal cells arranged in matrix form, and is further provided with a light-blocking region referred to as a black matrix, each cell being surrounded by the light-blocking region. A liquid crystal cell is a construction in which the space between two glass substrates, arranged such that surfaces on which transparent electrodes are formed confront each other, is filled with a liquid crystal material, and is capable of blocking or transmitting incident light by supplying voltage to the transparent electrodes to thus control the orientation of the liquid crystal molecules. When light is blocked by a liquid crystal cell, the liquid crystal molecules absorb the light, whereby the liquid crystal panel generates heat. In addition, the liquid crystal panel generates heat due to the absorption of light by the black matrix. The heat generation of the liquid crystal panel in some cases causes damage to the alignment film of the liquid crystal cells.
In addition, when a liquid crystal panel that operates in the TN (Twisted Nemantic) mode is used as the liquid crystal panel, sheet polarizers are provided on the incident surface side and emission surface side of the liquid crystal panel. These sheet polarizers transmit only light having a predetermined polarity component (for example, S-polarized light) and absorb other light. The absorption of light causes further heat generation in the sheet polarizers. The heat generation of the sheet polarizers in some cases causes a marked reduction of the polarizing selectivity characteristic of the sheet polarizers.
In response, cooling devices have been proposed for cooling liquid crystal panels and sheet polarizers. As technology related to the present invention, various liquid crystal projectors that incorporate such cooling devices are next described.
As an example of the related art, FIG. 1A is an external view of a liquid crystal projector and FIG. 1B is a perspective view showing the internal construction of the liquid crystal projector shown in FIG. 1A. FIG. 2 is a schematic view showing the configuration of the cooling device that is incorporated in this liquid crystal projector.
As shown in FIGS. 1A, 1B, and 2, liquid crystal unit 2, cooling fan 3, air-cooling ducts 4, light source 5, reflector 6, lamp cooling fan 7, lamp cooling duct 8, exhaust fan 9, power supply unit 10, and projection lens 11 are provided in the case of liquid crystal projector 1.
Light from light source 5 is reflected by reflector 6 and irradiated into liquid crystal unit 2 as parallel luminous flux. Liquid crystal unit 2 is provided with three liquid crystal panels that are each irradiated by luminous flux of each color that is color-separated into red (R), green (G), and blue (B) by a plurality of dichroic mirrors, and by a color-synthesizing prism for color synthesizing the image light of each color that has been modulated by the spatial arrangement by each liquid crystal panel. A sheet polarizer is provided on the incident surface side and emission surface side of each liquid crystal panel. Image light that has been color-synthesized by the color-synthesizing prism is projected onto a screen by projection lens 11.
Lamp cooling fan 7 and lamp cooling duct 8 are means for cooling light source 5. The airflow produced by lamp cooling fan 7 passes by way of lamp cooling duct 8 to reach light source 5. Cooling fan 3 and air-cooling duct 4 are means for cooling liquid crystal unit 2. The airflow generated by cooling fan 3 passes through air-cooling duct 4 to reach liquid crystal unit 2. Exhaust fan 9 exhausts air that is inside the housing to the outside.
FIG. 3A is an exploded perspective view showing the actual construction of a cooling device that cools liquid crystal unit 2, and FIG. 3B is a schematic sectional view for explaining the cooling operation in the cooling device shown in FIG. 3A.
As shown in FIGS. 3A and 3B, cooling device 15 includes air-cooling duct 4 and cooling fan 3. Air-cooling duct 4 is provided with a plurality of exhaust ports 17 for directing the airflow from cooling fan 3 toward liquid crystal unit 2. Liquid crystal unit 2 is arranged above exhaust ports 17.
Sheet polarizer 12 is arranged on the incident surface side of each liquid crystal panel 13 that makes up liquid crystal unit, and sheet polarizer 14 is arranged on the emission surface side (color-synthesizing prism side). Exhaust ports 17 are provided at each of the points made up from liquid crystal panel 13 and sheet polarizers 12 and 13.
As shown in FIG. 3B, ventilation air 16 from cooling fan 3 flows in air-cooling duct 4 and is directed toward liquid crystal unit 2 from each of exhaust ports 17. The airflow supplied from exhaust ports 17 cools liquid crystal panel 13 and sheet polarizers 12 and 14 by passing through each of the gaps of liquid crystal panel 13 and sheet polarizers 12 and 14.
JP-A-H11-295814 (hereinbelow referred to as Patent Document 1) discloses another form of a cooling device for cooling a liquid crystal unit. FIG. 4 is a schematic view showing the configuration of this cooling device.
Referring to FIG. 4, ventilation air 16 from cooling fan 3 flows between sheet polarizer 12 and liquid crystal panel 13 and between liquid crystal panel 13 and color-synthesizing prism 35. Flow-directing plate 39 is provided on a portion of the cooling fan 3 side of a member for holding color-synthesizing prism 35. By changing the direction of ventilation air 16 by means of flow-directing plate 39 such that ventilation air 16 from cooling fan 3 is directed toward the surface of liquid crystal panel 13, an improvement in the cooling efficiency of liquid crystal panel 13 can be achieved.
JP-A-2001-318361 (hereinbelow referred to as Patent Document 2) discloses yet another form of a cooling device for cooling a liquid crystal unit. FIG. 5 is a schematic view showing the configuration of this cooling device.
Referring to FIG. 5, two protruding members 41 are provided along the confronting rims of holding frame 40 of liquid crystal panel 13. Each protruding member 41 is a plate-shaped member and is controlled such that air supplied from duct exhaust port 42 flows in a fixed direction, whereby almost all air supplied from duct exhaust port 42 flows along the surface of liquid crystal panel 13 and thus improves cooling efficiency.
JP-A-2004-061894 (hereinbelow referred to as Patent Document 3) discloses yet another form of a cooling device for cooling a liquid crystal unit. FIG. 6 is a schematic diagram showing the configuration of this cooling device.
Referring to FIG. 6, slot 43 is formed in a portion of holding frame 40 of liquid crystal panel 13 that faces the airflow channel between liquid crystal panel 13 and sheet polarizer 14. The provision of slot 43 increases the width of the airflow channel (the widths shown by X and Y in FIG. 6), whereby the amount of airflow increases.
JP-A-2000-124649 (hereinbelow referred to as Patent Document 4) discloses yet another form of a cooling device for cooling a liquid crystal unit. FIGS. 7A and 7B are figures for explaining the configuration of this cooling device, FIG. 7A being an upper plan view and FIG. 7B being a side sectional view.
Referring to FIGS. 7A and 7B, air-guiding plate 44 having a U-shaped profile is installed between color-synthesizing prism 35 and sheet polarizer 12 arranged to confront each other with liquid crystal panel 13 interposed. The airflow from cooling fan 3 passes between color-synthesizing prism 35 and liquid crystal panel 13 and then is turned around by air-guiding plate 44. The airflow that was turned around by air-guiding plate 44 passes between liquid crystal panel 13 and sheet polarizer 12. This configuration enables the suppression of the occurrence of variations in temperature produced in the surface of liquid crystal panel 13.
Patent Document 4 further discloses a modification of the above-described cooling device. FIGS. 8A and 8B are figures for describing this modification, FIG. 8A being an upper plan view and FIG. 8B being a side sectional view. In this modification, cooling fan 3a is arranged below liquid crystal panel 13 and cooling fan 3b is arranged above liquid crystal panel 13. The airflow from cooling fan 3a passes between color-synthesizing prism 35 and liquid crystal panel 13. The airflow from cooling fan 3b passes between liquid crystal panel 13 and sheet polarizer 12. This modification can suppress the occurrence of variations in temperature that occur on the surface of liquid crystal panel 13.
JP-A-2001-209126 (hereinbelow referred to as Patent Document 5) discloses yet another form of a cooling device for cooling a liquid crystal unit. FIG. 9 is a sectional view giving a schematic representation of the configuration of this cooling device.
Referring to FIG. 9, the cooling device has an internal circulation portion provided with circulation duct 45 in which air flow generated by cooling fan 3a circulates and an external circulation portion provided with air circulation duct 46 in which air flow generated by cooling fan 3b circulates. Outside air is taken into the external circulation portion by cooling fan 3b. Air taken in by cooling fan 3b cools the internal circulation portion by flowing along the outer surfaces of circulation duct 45.